The present invention relates to novel printing ink binder resins, and more particularly to resinous products having a high softening point and high solubility to solvent useful for offset or letterpress ink binders.
A printing ink, especially an offset printing ink is generally required to have the following fundamental properties.
1. Values indicating the flow property, such as viscosity and yield value are adequate.
2. Interfacial balance between a damping water and an ink is maintained so that the ink can keep on the image areas of a plate.
3. A pigment is well dispersed.
4. Gloss of printed surfaces is good.
5. Setting and drying are quick and blocking does not take place.
6. Abrasion resistance of printed surfaces are good.
For giving the above properties to the printing ink, the following requirements are necessary for a resin used as a binder of printing ink.
1. Solubility to a high-boiling hydrocarbon solvent and drying oil is enough.
2. Softening point is high and viscosity of the obtained varnish is high.
3. A functional group is temperately present.
4. Color is light color.
Hitherto, varnishes for offset printing ink are generally prepared by dissolving a resin such as alkylphenol resins, rosin-modified phenol resins or ester gum in a high-boiling solvent such as aliphatic hydrocarbons having a boiling point of 240.degree. to 330.degree. C. and an aniline point of 65.degree. to 100.degree. C. and/or a drying oil such as linseed oil, tung oil, dehydrated castor oil or safflower oil, and such varnishes are widely employed. In recent year, the printing speed becomes higher and, therefore, printing inks applicable to high-speed printing and capable of providing excellent gloss are desired. According to these desires, various binders for printing ink are proposed. One of them is a rosin type resin and it is considered to be suitable for the resin used as a binder of offset printing inks. However, these binders are not necessarily satisfactory. Other resins as a binder proposed have also the disadvantages. For instance, Japanese Patent Publication No. 27,492/1971 discloses a resin prepared by reacting a petroleum resin having a softening point of 58.degree. C. with a phenol-formaldehyde pre-condensate in the presence of maleic anhydride and a esterification product of the resin with glycerin. However, since the softening points of these resins are low, the viscosity of the varnish prepared therefrom is low. Also the solubility of these resins to a high-boiling aliphatic hydrocarbon solvent is poor, and moreover the resins are unsuitable as a binder for light color printing ink since they are colored. It is also proposed in Japanese Patent Public Disclosure No. 24,405/1972 to use a binder resin prepared by reacting a maleic acid-modified cyclopentadiene polymer, a higher fatty acid and a polyhydric alcohol. Printing inks prepared from the resin have the disadvantages that the setting time is long due to low softening point of the resin and the gloss is insufficient. Japanese Patent Public Disclosure No. 82,405/1974 discloses a binder resin prepared by reacting a heat-polymerized cyclopentadiene modified with maleic acid with a phenol-formaldehyde precondensate. Such a binder resin is also unsatisfactory because the setting time is long and the gloss is poor.